A pipe 1 yard long holds approximately (actually, 1·52 per cent. less) as many pounds of water as the square of its diameter in inches; thus a 6-inch pipe holds approximately 36 lbs. of water in each yard length. _Water Pressure._ Ten feet head of water gives a pressure of 4½ lbs. per square inch approximately. If H = head of water in feet, P = pounds pressure per square inch: H = P × 2·311 P = H × ·4326 _Horse-power required to Pump Water._--One h.-p. indicated will raise about 3000 gallons of water per hour 50 feet high. To pump 1 gallon of water per minute against a pressure of 4 lb. per square inch, requires: p × ·0007 H.-P. BORING. Rock is bored with jumpers of 10 lb. to 18 lb., used alone, or with boring bars and hammer. The former are more effective, but can only be used perpendicularly, or nearly so, and with rock of moderate hardness; they require more skill. 18 lb. hammers are used for 3 in. boring bars. 16 lb. ” ” 2½ in. ” 14 lb. ” ” 2 & 1¾ in. ” 5-7 lb. ” ” 1 in. ” The boring bars may be made of 1-1/8-inch bar iron of various lengths, with steel bits up to 3 inches. A bit should bore from 18 feet to 24 feet with each steeling, and requires to be sharpened once for every foot bored. 3 men with a 3-inch bar should bore 4 feet. 3 ” ” 2½ ” ” ” 6 ” 3 ” ” 2 ” ” ” 8 ” 3 ” ” 1¾ ” ” ” 12 ” 2 ” ” 1 ” ” ” 8 ” per day of 10 hours in hard granite. POWER, ETC., REQUIRED TO WORK ROCK DRILLS. +-----+----------+----------+--------+---------------+ | | Diameter | Diameter | | No. of | |H.-P.| of Air | of Steam | Stroke.| 3-inch Drills | | | Cylinder.| Cylinder.| | driven. | +-----+----------+----------+--------+---------------| | | Inches. | Inches. | Inches.| | | 6 | 8 | 8½ | 12 | 1 | | 10 | 10 | 10½ | 16 | 2 | | 14 | 12 | 12¼ | 22 | 3 | | 16 | 13 | 13 | 24 | 4 | | 20 | 14½ | 14½ | 28 | 5 | | 30 | 17½ | 17½ | 36 | 8 | | 40 | 20 | 20 | 36 | 11 | | 60 | 22 | 24 | 60 | 15 | +-----+----------+----------+--------+---------------+ POWER REQUIRED TO WORK DOUBLE STEAM AND AIR CYLINDERS.